High-quality radio reception in Europe has previously been attainable only with VHF transmitters. On the medium-wave or AM broadcast band, conversely, the audio quality is poor because of the low-frequency bandwidth of 4.5 kHz, which is limited by the 9 kHz channel separation or allocation pattern provided by government regulations, for example in Germany.
With only a few exceptions, medium-wave or AM transmitters were previously used for supraregional service to areas that were beyond the range of the VHF transmitters. The AM program was also broadcast over the VHF transmitters, however.
To widen the range of programs, an article by H. Fritsch, entitled "Mittelwelle, Akzeptanz durch mehr Klang" (which translates into English as: Broader Acceptance Through Better Sound), in the Journal Funkschau [Broadcast Review] 1990, No. 3, pp. 40-45, proposes sending AM's "own" programs over the AM band as well. The plan is to use a wider low-frequency bandwidth than has previously been the case in broadcasting. Experiments are intended to find out how this could be done, for which transmitters and frequencies and at what times of day, without disturbing adjacent transmitters.
Once these experiments are completed, if a broad-band program is broadcast by various transmitters, then there will in the future be two types of transmitters, in the medium-wave range and perhaps in the long-wave range as well. One type of transmitter functions as before with a normal bandwidth, which fits into the usual 9 kHz pattern; the other transmitters will operate with bandwidth expansion.
To be able to receive the programs in the quality offered in each case, a departure from the previous design for radio receivers for a fixed intermediate frequency bandwidth must be made. Instead, the capacity for switchover of the IF filter must be provided, to attain optimal reception results in each case.
Although manual switchover is possible and is intrinsically conceivable, it is inconvenient, because varying medium-wave broadcasting conditions can engender fluctuations in the reception quality; when transmitters with an expanded bandwidth are received, these fluctuations can necessitate a switchover of the IF filter to a narrower bandwidth even while a transmission is in progress. This can be expected especially in vehicle radios, with increasing distance from where the transmitter is located.